can't access admin page?

Hello everyone:
I used my own theme.
When I access admin page,the url is http://192.168.209.136/Marx/Security/login?BackURL=%2FMarx%2Fadmin%2Fpages
after click login button,the url is http://192.168.209.136/Marx/Security/Security/LoginForm.
and the content of page now is:
Action 'Security' isn't available on class Security.

I suppose that my theme has something wrong ,so I rename de default theme 'simple' to my own theme's name 'Marx'.
but the page doesn't change into 'simple' style,and the admin page still cannot access.

Therefore, all images in my article are missing too.I use "src='assets/images/pic1.jpg'".
in the homepage ,all images are ok.
but in the sub-page,the image's url will change into "page-0/assets/images/pic1.jpg'".

Im very new to SS,
Also can't access admin page, after migration to the live server and trying to access http://DomainName/admin it redirects me to
http://DomainName/Security/login?BackURL=%2Fadmin%2Fpages and im seeing the login form of silverstripe being rendered on the $Layout section of Page.ss

and when i try to login, it show "Sorry, it seems you were trying to access a page that doesn't exist"
I attached a picture for clarification.
Any suggestion is appreciated.
Thank you!